A light-emitting diode (referred to hereinafter as LED) represents one of the most popular light-emitting devices today. Due to the high power efficiency and small form factors, LEDs are commonly used not only in light-emitting devices, but also other devices such as flat panel display systems, optical transmitters, optocouplers, electronic sign and display systems, indicator lights, optical encoders and many other similar optical devices. Optical encoders, opto-couplers and proximity sensors may also be known as optical sensors. The LED dies are typically less than 1 mm in size. The small size enables integration of an optical lens into the optical devices. For example, many optical devices, such as optical encoders and proximity sensors have integrated lens. Some lighting fixtures may also comprise a lens.
By collimating, focusing and directing light emitted from the LED light source dies in a specific direction the lens may be configured to increase optical efficiency by approximately 3 times when compared to a device without an optical lens. For example, a light source die in an optical encoder may emit light in all directions, but by using appropriate reflectors and lenses, the light may be focused and channeled to the code wheel, and thus, increasing the power efficiency. In addition, the optical lens may be configured to transform the resolution of a code wheel in order to match the spacing of the photodiodes. For example, the light signals reflected from a code wheel may comprise light bars distanced away from each other in a first dimension different from the spacing between photodiodes resolution, which is in a second dimension. However, the resolution of the light bars, after going through a lens, may be altered into the second dimension matching the spacing between photodiodes resolution. As a result, by using a lens, one type of photodiode with a specific dimension may work with many different code wheels having different resolutions.
Optical lenses may be manufactured using epoxies or any other transparent encapsulant materials commonly used to encapsulate the LED light source dies. Generally, an optical lens may be pre-formed and then glued to the optical device. Optionally, the optical lens may be attached to an encapsulant material in a semi-liquid form followed by a curing process. The above-mentioned method is widely used in making optical sensors and devices, such as proximity sensors, optical encoders, light-emitting devices and many other similar devices.
However, the molding process if not done carefully may result in reliability issues such as delamination and trapping of air bubbles at the area near the lens. The encapsulant used to form the lens is made from liquid or semi-liquid form before being cured into solid form. As the encapsulant is used to fill up a cavity or a reflector cup commonly used in a light-emitting device, air bubbles might be trapped inside the device. In the case where the lens is attached utilizing glue, the lens may be detached when exposed to heat, because different materials in the lens and the body may have different thermal expansion and contraction properties. In addition, a thin layer of air may be trapped in the gluing process and thus deteriorate the optical property of the devices.